Which among the following have open circulatory system?
(i) Arthropoda (ii) Mollusca
(iii) Annelida (iv) Coelenterata

Options

A. (i) and (ii)
B. (iii) and (iv)
C. (i) and (iii)
D. (ii) and (iv)

Explanation

To determine which among the given groups of organisms have an open circulatory system, we can analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Open Circulatory System**:
- An open circulatory system is characterized by the blood (or hemolymph) being pumped into open spaces (hemocoel) where it directly bathes the organs. There are no capillaries to separate the blood from the tissues.

2. **Analyzing the Options**:
- **(i) Arthropoda**: This group includes insects, arachnids, and crustaceans. They possess an open circulatory system where the hemolymph flows freely around the organs.
- **(ii) Mollusca**: This group includes snails, clams, and octopuses. Most mollusks also have an open circulatory system, although some cephalopods (like octopuses) have a closed system.
- **(iii) Annelida**: This group includes segmented worms like earthworms. Annelids typically have a closed circulatory system, with blood contained within vessels. However, leeches (a type of annelid) do have an open circulatory system.
- **(iv) Coelenterata**: This group includes organisms like jellyfish and corals. They do not have a true circulatory system; instead, they rely on diffusion for nutrient and gas exchange.

3. **Identifying the Correct Options**:
- From the analysis, we see that both Arthropoda and Mollusca generally have an open circulatory system.
- Annelida and Coelenterata do not typically have an open circulatory system.

4. **Conclusion**:
- The organisms that have an open circulatory system among the options provided are **(i) Arthropoda** and **(ii) Mollusca**.

### Final Answer:
The correct answer is **(i) Arthropoda and (ii) Mollusca**.